Bypass air valve for a gas turbine

ABSTRACT

A bypass air valve is provided comprising a liner, a strap, and apparatus for selectively actuating the valve. The liner includes an inner surface, an outer surface, a plurality of first regions, and a plurality of second regions. Each first region includes a plurality of first apertures. The strap includes a plurality of openings and a plurality of third regions. The third regions include a plurality of second apertures. The valve may be selectively actuated into an open position where the first regions are in communication with the openings, and the third regions are in communication with the second regions. The valve may be selectively actuated into a closed position where the first regions are in communication with the third regions, and the second regions are in communication with the openings. The flow path through the first and second apertures in the closed position impedes flow substantially more than the flow path through the first apertures and the openings in the open position, thereby effectively closing bypass air flow through the valve in the closed position.

The invention was made under a U.S. Government contract and theGovernment has rights herein.

BACKGROUND OF THE INVENTION

1. Technical Field

This invention applies to gas turbine engines in general, and to bypassair valves in particular.

2. Background Information

The amount of thrust produced by a gas turbine engine may be describedin terms of the "power setting" of the engine. In the case of a gasturbine driven aircraft, higher power settings can provide additionalthrust when necessary to satisfy aircraft performance requirements.Increasing power settings, however, increases core gas flowtemperatures, and consequent cooling requirements within the engine. Tosatisfy the cooling requirements, inlet air is pressurized, separatedfrom the core gas flow and subsequently bled into the core gas flow atvarious positions within the engine. The work of pressurizing the inletair (also known as "bypass air") is lost as the air passes from one ormore bypass ducts, through cooling apertures, and into the core gasflow. Hence, the efficiency of the engine is effected by the amount ofinlet air used for cooling purposes.

Bypass air selectively introduced into the core gas flow through bypassair valves can minimize the work lost during cooling. At lower powersettings, cooling requirements are less and bypass air may be "dumped"through less restrictive bypass air valves rather than the morerestrictive aforementioned cooling apertures. Currently available bypassair valves are not without problems, however. Peak power settingsnecessitate large amounts of bypass air be used to cool the engine. Abypass air valve that allows more bypass air through the valve than isnecessary to cool the valve in the closed position, decreases downstreamcooling capacity and therefore the engines ability to run at peak power.

In addition, thermal growth within the engine makes effective sealing aproblem. A bypass air valve "loose" enough to accommodate thermal growthwill likely leak significantly in the closed position and negativelyeffect the performance of the engine. A bypass air valve "tight" enoughto seal, on the other hand, may bind as a result of thermal expansion ormay require a significant actuation force due to friction and largenormal forces between the strap and the liner. Normal forces can becomerather large when the pressure forces acting against the strap are addedto the forces resulting from the thermal expansion of the liner.

Complexity and weight are still further problems of some present bypassair valves. Flap valves, for example, have been designed which properlyseal despite the harsh thermal environment, but do so at the cost ofsimplicity. Flap valve systems typically employ a plurality of flapvalves disposed about the circumference of the liner, each requiring aflap, a hinge mechanism, and an actuating mechanism. A collectiveactuator is also required to ensure that all flaps operate in concert.Such a system, although operational, unnecessarily adds to thecomplexity and weight of the engine. Complexity is also generallyinversely related to cost and reliability.

What is needed, therefore, is a lightweight, simple, bypass air valvethat prevents bypass air from entering the core gas flow when closed,and which can be easily actuated into an open position, and whichaccommodates high thermal loads without adverse consequences.

DISCLOSURE OF THE INVENTION

It is an object of the present invention, therefore, to provide a bypassair valve that is simple and lightweight.

It is another object of the present invention to provide a bypass airvalve that adequately accommodates high thermal loads with negligiblethermal distortion and\or burnout.

It is another object of the present invention to provide a bypass airvalve that can accommodate axial and circumferential pressure gradientswithin the core gas flow in the region of the valve.

According to the present invention, a bypass air valve is providedcomprising a liner, a strap, and means for selectively actuating thevalve. The liner includes an inner surface, an outer surface, aplurality of first regions, and a plurality of second regions. Eachfirst region includes a plurality of first apertures. The strap includesa plurality of openings and a plurality of third regions. The thirdregions include a plurality of second apertures. The valve may beselectively actuated into an open position where the first regions arein communication with the openings, and the third regions are incommunication with the second regions. The valve may be selectivelyactuated into a closed position where the first regions are incommunication with the third regions, and the second regions are incommunication with the openings. The flow path through the first andsecond apertures impedes flow substantially more than the flow paththrough the first apertures and the openings, thereby effectivelyclosing bypass air flow through the valve.

An advantage of the present invention is that a simple and lightweightbypass air valve is provided. The liner, strap, and selective actuatorof the present invention obviate the need for a plurality of doors anddoor actuating hardware. The strap and liner of the present inventionare also simpler to manufacture and lighter in weight than existingbypass air valves.

A further advantage of the present invention is that bypass air isuniformly introduced into the core gas flow. The present bypass airvalve allows bypass air to be introduced around the entire circumferenceof the liner as opposed to the few discrete positions available whenflaps are used. The more uniform distribution promotes efficientcombustion downstream.

A still further advantage of the present invention is that flowimpediments within either the bypass air path or the core gas path areminimized. Flap-type bypass air valves generally extend one or moreflaps into one of the bypass air or core gas paths and therefore impedeflow within that path. A person of skill in the art will recognize thatit is desirable to minimize most gas flow impediments.

A still further advantage of the present invention is the ability of thevalve to accommodate axial and circumferential pressure gradients withinthe core gas flow in the region of the valve.

These and other objects, features, and advantages of the presentinvention will become apparent in light of the detailed description ofthe best mode embodiment thereof, as illustrated in the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic view of a gas turbine engine.

FIG. 2 is a diagrammatic view of the present invention bypass air valve.

FIGS. 3A--3D are enlarged partial views of the present invention bypassair valve. FIG. 3A shows the valve in the closed position. FIG. 3B showsthe valve being actuated toward the open position. FIG. 3C shows thevalve in the open position. FIG. 3D shows the valve being actuatedtoward the closed position.

FIG. 4 shows a top view of FIG. 3A.

FIG. 5 shows a portion of the strap and liner of the present inventionin the closed position.

FIG. 6 is a cross-sectional view of FIG. 5.

FIG. 7 shows a portion of the strap and liner of the present inventionin the open position.

FIG. 8 is a cross-sectional view of FIG. 7.

FIG. 9 is a cross-sectional view of FIG. 5.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring to FIG. 1, a gas turbine engine 10 may be described as havinga fan 12, a compressor 14, a combustor 16, a turbine 18, a bypass airvalve 20, an augmentor 22, and a nozzle 24. Air exiting the fan 12 isdivided between core gas flow 26 and bypass air flow 28. Core gas flow26 follows a path through the compressor 14, combustor 16, turbine 18,augmentor 22, and nozzle 24 in that order. Core gas flow 26 may,therefore, be described as following a path substantially parallel tothe axis 30 of the engine 10. Bypass air 28 also follows a path parallelto the axis 30 of the engine 10, passing through an annulus 32 extendingalong the periphery of the engine 10. Aft of the turbine 18, bypass airflow 28 is at a higher pressure than core gas flow 26.

I. Elements of the Bypass Air Valve

FIGS. 2-4 show diagrammatic views of a bypass air valve 20. The bypassair valve 20 is positioned to receive bypass air 28 passing through theannulus 32. The bypass air valve 20 includes a strap 34, a liner 36,means 38 for biasing the strap 34 in contact with the liner 36, aselective actuator 40, and means 42 for the passage of bypass air 28(see FIG. 4). The liner 36 includes an inner 44 and an outer 46 surface.The inner surface 44 is exposed to core gas flow 26. The strap 34 isformed in a ring having a width 48, a length 50, a first flange 52attached to a lengthwise end of the strap 34, and a second flange 54attached to the other lengthwise end of the strap 34.

Referring to FIGS. 3A-3D and 4, the means 38 for biasing the strap 34 incontact with the liner 36 includes a pair of spring assemblies 56. Eachspring assembly 56 includes a spring 58, a bolt 60, and a nut 62. Thebolt 60 extends through the spring 58 and through clearance holes in thefirst 52 and second 54 flanges. The spring 58 acts between the boltnut60,62 assembly and the outer surface 64,66 of one of the flanges 52,54.FIGS. 3A-3D and 4 show the springs 58 acting between the nuts 62 and theouter surface 64 of the first flange 52.

Referring to FIGS. 5-9, the strap 34 may include a structural member 68attached to the side of the strap 34 facing away from the liner 36. Thestructural member 68 includes an outer ring 70 and a corrugated ring 72.The corrugated ring 72 extends between the strap 34 and the outer ring70 and is attached to both by conventional means. In the preferredembodiment, the outer ring 70 and the corrugated ring 72 includeopenings 74 to enhance bypass air 28 distribution in the area of thestructural member 68.

Referring to FIGS. 3A-3D and 4, the selective actuator 40 includes anarm 75 and a driver 76. The arm 75 includes a first outer bar 78, asecond outer bar 80, and a middle bar 82 disposed between the outer bars78,80. The outer bars 78,80 are spaced equidistant from the middle bar82. The first flange 52 of the strap 34 is disposed between the middlebar 82 and the second outer bar 80. The second flange 54 of the strap 34is disposed between the middle bar 82 and the first outer bar 78. Theend 83 of the arm 75 opposite the bars 78,80,82 is pivotly attached tothe driver 76. The arm 75 further includes a joint 84 to accommodate anymisalignment between the driver 76 and the strap 34.

Referring to FIGS. 5-8, the means 42 for passage of bypass air 28includes a plurality of first 86 and second 88 regions disposed in theliner 36, and a plurality of openings 90 and third regions 92 disposedin the strap 34. FIGS. 5 and 6, and FIGS. 7 and 8 show the strap 34 andthe liner 36 in the closed and open positions, respectively. Each of thefirst regions 86 includes a plurality of first apertures 94 extendingthrough the liner 36 and counterbores 96 disposed within the outersurface 46 of the liner 36. In the preferred embodiment, the firstapertures 94 are triangularly arranged in groups of three, with thegroups aligned in parallel rows. A counterbore 96 is disposed withineach group of three first apertures 94, overlapping each aperture 94.The second regions 88 include a plurality of fins 98 disposed inparallel rows, formed within the outer surface 46 of the liner 36. Thethird regions 92 include a plurality of second apertures 100 extendingthrough the strap 34, arranged in parallel rows. The cross-sectionalarea of the openings 90 in the strap 34 is substantially the same asthat of the first 86 or second 88 regions or larger.

In the preferred embodiment, the first 86 and second 88 regions in theliner 36 are arranged in a "checkerboard" pattern, where the first 86and second 88 regions alternate both axially and circumferentially.Likewise, the third regions 92 and the openings 90 in the strap 34 arealso arranged in a checkerboard pattern, where the third regions 92 andthe openings 90 alternate axially and circumferentially.

II. The Bypass Air Valve in the Closed Position

Referring to FIGS. 5-8, in the operation of the bypass air valve 20, thevalve 20 is normally closed which forces most of the bypass air 28 tocontinue downstream to cool the augmentor 22 and the nozzle 24 (see FIG.1). In the closed position, the openings 90 within the strap 34 arealigned with and above the second regions 88 of the liner 36 and thethird regions 92 of the strap 34 are aligned with and above the firstregions 86 of the liner 36. The third regions 92 are aligned with thefirst regions 86 such that a row 102 of second apertures 100 liesbetween adjacent rows of first aperture 94 groups and a row 104 ofsecond apertures 100 is aligned with each row of first aperture 94groups. The strap 34 is biased in contact with the liner 36 by both thespring assemblies 56 (see FIG.4) and the pressure difference across theliner 36 and strap 34. The spring assemblies 56 enable the valve 20 toaccommodate disparate thermal growth between the strap 34 and the liner36 without binding.

In the closed position, some bypass air 28 traveling within the annulus32 enters the openings 90 within the strap 34, and travels between therows of fins 98 formed within the second regions 88. In the preferredembodiment, the fins 98 are oriented at a 45° angle relative to thebypass air flow 28 to enhance heat transfer from the fins 98 to thebypass air flow 28. Referring to FIG. 6, other bypass air 28 is drawninto the second apertures 100 by the pressure difference across thestrap 34 and liner 36. A portion of the bypass air 28 drawn into secondapertures 100 enters the rows 102 of second apertures 100 positionedbetween the rows of first aperture 94 groups. Normally, these secondapertures 100 do not provide further passage for bypass air because thestrap 34 and liner 36 are biased in contact with one another. In theevent the strap 34 is thermally distorted and a gap (not shown) developsbetween the strap 34 and the liner 36, however, these second apertures100 provide a flow path for auxiliary cooling of the liner 36 andthereby prevent hot gas influx and potential burnout. The remainder ofthe bypass air flow 28 entering the second apertures 100 enters thoserows 104 aligned with the first aperture 94 groups. Bypass air 28entering these rows 104 of second apertures 100 passes into thecounterbores 96 and subsequently through the first apertures 94. As canbe seen in FIG. 6, bypass air 28 must travel within the counterbores 96before entering the first apertures 94 due to the misalignment of thefirst 94 and second 100 apertures. An advantage of deploying secondapertures 100 in rows 104 is that some circumferential misalignmentbetween the first aperture 94 groups and the second apertures ispermissible. Specifically, the frequency of the second apertures 100 isgreat enough such that a sufficient number of second apertures 100 willalways be aligned with each of the first aperture 94 groups.

The pressure difference between the bypass air flow 28 and the core gasflow 26, is discretely stepped across the strap 34 and across the liner36. The discrete steps are made possible by the diameter of each secondaperture 100 in the strap 34 being approximately five times smaller thanthe diameter of each first aperture 94 in the liner 36. The smallersecond apertures 100 support a much larger pressure difference than dothe larger first apertures 94. As a result, bypass air flow 28 "jets"into the counterbores 96 from the second apertures 100 and "bleeds" outof the first apertures 94. The bypass air 28 jets acting on thecounterbores 96 create impingement cooling of the liner 36. The lowpressure bleeding of the bypass air 28 from the first apertures 94facilitates the formation of a boundary layer (not shown) along theinner surface 44 of the liner 36. The boundary layer of relatively coolbypass air 28 helps to thermally protect the liner 36 from the hot coregas flow 26 (see FIG. 1). The difference in diameter between the first94 and second 100 apertures may be increased or decreased to alter themagnitude of the pressure steps across the strap 34 and liner 36.

The first 94 and second 100 apertures and counterbores 96 alsocompartmentalize flow through the valve 20. Flow 28 entering acounterbore 96 through one or more aligned second apertures 100 mustexit the first apertures 94 in communication with that counterbore 96.As a result, the first apertures 94 have a positive flow of bypass air28 exiting them despite having only a slight difference in pressureacross them. The positive air flow through the first apertures 94 isparticularly important in areas where the pressure distribution withinthe core gas flow 26 is irregular and at points may exceed the pressureof a local counterbore 96. In that instance, bypass air 28 will enterthe counterbore 96 by virtue of the relatively large pressure differenceacross the strap 34, and increase in pressure until the pressure withinthe counterbore 96 exceeds the local pressure within the core gas flow26. Hence, hot gas influx and potential burnout are avoided.

III. Actuating the Valve Toward the Open or Closed Position

Referring to FIGS. 3A-3D, when the valve 20 is actuated toward the openposition, the driver 76 drives the arm 75 in a direction substantiallytangential to the circumference of the liner 36. As a result, the middlebar 82 contacts the first flange 52 and drives a segment of the strap 34out of contact with the liner 36 (see FIG. 3B). The length of thesegment depends upon the stiffness of the strap 34 and the magnitude ofthe forces biasing the strap 34 against the liner 36. After the strapsegment has been disengaged from the liner 36, the strap 34 will betranslated by either the spring assemblies 56 drawing the second flange54 in the same direction, or by the first outer bar 78 contacting thesecond flange 54. After the strap 34 is translated to the open position,the spring assemblies 56 and the pressure against the strap 34 will biasthe strap 34 against the liner 36 (see FIG. 3C).

When the valve is actuated toward the closed position, the driver 76drives the arm 75 in a direction opposite that taken to open the valve20. In doing so, the middle bar 82 contacts the second flange 54 anddrives a segment of the strap 34 out of contact with the liner 36 (seeFIG. 3D). The strap 34 is subsequently translated by either the springassemblies 56 drawing the first flange 52 in the same direction, or bythe second outer bar 80 contacting the first flange 52. After the strap34 is translated to the open position, the spring assemblies 56 and thepressure against the strap 34 bias the strap 34 against the liner 36(see FIG. 3A).

IV. The Bypass Air Valve in the Open Position

In the open position, the openings 90 in the strap 34 are aligned withand above the first regions 86 in the liner 36, and the third regions 92in the strap 34 are aligned with and above the second regions 88 in theliner 36. The openings 90 allow a large volume of bypass air 28 to passdirectly through the first apertures 94 into the core gas flow 26. Thedistribution of first regions 86 around the circumference of the liner36 enables bypass air 28 to be uniformly introduced into the core gasflow 26

Although this invention has been shown and described with respect to thedetailed embodiments thereof, it will be understood by those skilled inthe art that various changes in form and detail thereof may be madewithout departing from the spirit and the scope of the invention. Forexample, the preferred arrangement of regions 86,88,92 and openings 90within the means 42 for the passage of bypass air 28 is given as acheckerboard pattern. Other patterns may be used alternatively. A stillfurther example is the preferred grouping of three first apertures 94and a counterbore 96. More or less than three first apertures 94 couldbe used alternatively.

I claim:
 1. A bypass air valve, comprising:a liner, having an outersurface, a plurality of first regions, each first region including aplurality of first apertures, and a plurality of impermeable secondregions; a strap, surrounding said liner, having a plurality of openingsand a plurality of third regions, said third regions including aplurality of second apertures; means for selectively actuating saidvalve; wherein said valve may be selectively actuated into an openposition where said first regions are substantially aligned with saidopenings and said third regions are substantially aligned with saidimpermeable second regions, thereby providing a first flow path forbypass air surrounding said valve to pass through said valve via saidopenings and first apertures; and wherein said valve may be selectivelyactuated into a closed position where said first regions aresubstantially aligned with said third regions and said second regionsare substantially aligned with said openings, thereby providing a secondflow path for bypass air surrounding said valve through said valve viasaid second and first apertures, and exposing said second regions tosaid bypass air surrounding said valve; and wherein said second flowpath is sized to impede passage of bypass air through said valvesubstantially more than said first flow path.
 2. A bypass air valveaccording to claim 1, wherein said first regions further comprise:aplurality of counterbores disposed within said outer surface, whereineach said counterbore is substantially aligned with at least one of saidfirst apertures.
 3. A bypass air valve according to claim 2, whereinsaid first apertures are disposed in groups, said groups aligned in aplurality of parallel rows;wherein each said group includes one of saidcounterbores disposed within said group, said counterbore overlappingeach of said first apertures in said group.
 4. A bypass air valveaccording to claim 3, wherein each said first aperture group includesthree of said first apertures triangularly disposed.
 5. A bypass airvalve according to claim 3, wherein in said closed position, a first rowof second apertures is disposed in line with each said row of said firstaperture groups, and a second row of said second apertures is disposedbetween adjacent rows of first aperture groups.
 6. A bypass air valveaccording to claim 5, wherein three second apertures align with eachsaid counterbore in said closed position.
 7. A bypass air valveaccording to claim 6, wherein said first and second regions are disposedalternately about the circumference of said liner.
 8. A bypass air valveaccording to claim 7, wherein said first and second regions are disposedalternately in an axial direction with said liner.
 9. A bypass air valvebleed according to claim 8, wherein said openings and said third regionsare disposed alternately about the circumference of said strap.
 10. Abypass air valve according to claim 9, wherein said openings and saidthird regions are disposed alternately in an axial direction with saidstrap.
 11. A bypass air valve according to claim 10, wherein firstapertures are larger in diameter than said second apertures.
 12. Abypass air valve according to claim 11, wherein each said first aperturegroup includes three of said first apertures triangularly disposed. 13.A bypass air valve according to claim 1, wherein said impermeable secondregions include heat transfer surfaces formed within said outer surfaceof said liner.
 14. A bypass air valve according to claim 13, whereinsaid heat transfer surfaces comprise a plurality of fins arranged inparallel rows.
 15. A bypass air valve according to claim 14, whereinsaid first regions further comprise:a plurality of counterbores disposedwithin said outer surface wherein each said counterbore is substantiallyaligned with at least one of said first apertures.
 16. A bypass airvalve according to claim 15, wherein first apertures are larger indiameter than said second apertures.
 17. A bypass air valve according toclaim 16, wherein said first apertures are disposed in groups, saidgroups aligned in a plurality of parallel rows;wherein each said groupincludes one of said counterbores disposed within said group, saidcounterbore overlapping each of said first apertures in said group. 18.A bypass air valve according to claim 17, wherein each said firstaperture group includes three of said first apertures triangularlydisposed.
 19. A bypass air valve according to claim 18, wherein in saidclosed position, a first row of second apertures is disposed in linewith each said row of said first aperture groups, and a second row ofsaid second apertures is disposed between adjacent rows of firstaperture groups.
 20. A bypass air valve according to claim 19, whereinthree second apertures align with each said counterbore in said closedposition.
 21. A bypass air valve according to claim 20, wherein saidfirst and second regions are disposed alternately about thecircumference of said liner.
 22. A bypass air valve according to claim21, wherein said first and second regions are disposed alternately in anaxial direction with said liner.
 23. A bypass air valve according toclaim 22, wherein said openings and said third regions are disposedalternately about the circumference of said strap.
 24. A bypass airvalve according to claim 23, wherein said openings and said thirdregions are disposed alternately in an axial direction with said strap.